It is often times imperative to be able to monitor the relative quantities of a microingredient, such as a drug or nutrient, in a bulk material for a number of reasons. For example, the United States Food and Drug Administration provides for the addition of selenium in the form of sodium selenite or selenate to certain animal feeds, but only if it is added as a premix containing not more than 200 ppm selenium. In that selenium at relatively low concentrations in feeds (i.e., 5 ppm) is exceedingly toxic, the Food and Drug Administration requires that each batch of animal feed premix be analyzed for selenium content, which is, needless to say, a laborious and time-consuming task. As such, it is clearly useful to develop a method that would permit a specific microingredient to be readily separated from the bulk material, so that it could then be analyzed free from those analytical interferences generally contributed by the bulk material. As concerns selenium such a method would permit the determination of selenium as the FDA-permitted selenite or selenate. No existing analytical procedure distinguishes selenite and selenate from other selenium compounds that may occur or be added to animal feed premixes. Similarly such a method would permit distinguishing among like generic drugs or nutrients from different sources.
As a means of accomplishing the above, Applicant disclosed for the first time in U.S. Pat. No. 4,152,271 a ferromagnetic tracer particle which could be separated from the bulk mix much faster and easier than prior tracers by means of magnetic separators. The various advantages inherent in the use of such materials became readily apparent. It was noted that the use of the tracer in conjunction with a magnetic separator permitted examination of large samples of bulk materials avoiding the restriction to small samples required when sedimentation separation procedures were employed.
The vehicle for the tracer disclosed in Applicant's prior U.S. Pat. No. 4,152,271 was taught to consist of ground, soft iron or other ferromagnetic material that could be magnetized by a magnetic field, but which would lose its magnetism in the absence of such a field. The ferromagnetic particle was made easily identifiable by having an FD & C Color or other permitted distinguishable microingredient adsorbed on the ferromagnetic material. Since the tracer particles were to be counted, even major losses of the distinguishing adsorbed layer to the bulk material by abrasion or diffusion could be tolerated without loss of accuracy in the particle count.
It is the object of the present invention to incorporate the microingredient within the particle itself so that in separating the particle from the bulk material essentially 100% of the specific microingredient would also be separated and thus freed from the bulk material.
It is a further object of the present invention to provide a tracer particle which could carry a microingredient in a bulk mixture and yet could be retrieved for analytical testing with the assurance that substantially none of the microingredient had inadvertently separated from the tracer.